Construction of chimeric insecticidal proteins between the 130-kDa and 135-kDa proteins of Bacillus thuringiensis subsp. aizawai for analysis of structure-function relationship.

Eight chimeric insecticidal protein (IP) genes were constructed between the 130-kDa and 135-kDa IP genes of Bacillus thuringiensis subsp. aizawai, and expressed in Escherichia coli JM103 cells. The characterization of the produced chimeric IPs indicated that the variable region (VR1) in the amino-terminal half of the IPs is responsible for the insecticidal activity against larvae of Spodoptera litura and Plutella xylostella. The carboxy-terminal half of VR1 was important for the formation of the 60-kDa active fragment in the gut juice of S. litura larvae. Also, combination of the other two variable regions (VR2 and VR3), which were in the central and carboxy-terminal portions of the IPs, appeared to be related to the solubility of the IPs in the gut juice.